Free piston machine



Nov. 17, 1959 J. s. CAMPBELL 2,912,965

FREE. PIs'roN MACHINE Filed July 14', 195e `ATTORNEY v 2,912,965 FREEPIsroN MACHINE James S. Campbell, Kingston, Ontario, Canada, assignertoQueens University, Kingston, Ontario, Canada Application July '14,1958, Serial No. 748,312

2 Claims. l (C1. 12S-H46) This invention relates to free piston machinessuch as compressors and gasifiers.

IIn conventional free piston gasifiers and compressors,

the pistons are returned after the firing stroke by energy stored inbounce cylinders in which air is trapped and compressed.

In compressing air part of the energy absorbed in the air is transferredto heat and lost. Moreover, piston rings are depended upon to trap theair and these are not fully eicient as a result of which it is usual toreplace the lost air after every stroke. The mechanism necessary toeffect this step further complicates the mechanical arrangement of thestructure design.

It is an object of this invention to provide a simple mechanical meansof greater efl'iciency for returning the pistons of a free pistonstructure after the firing stroke.

To this end, the invention contemplates the provision, in a free pistonmachine having a pair of piston assemblies, of a mechanical springarranged to store energy in response to the firing stroke of each pistonassembly, such spring on completion of the firing stroke being arrangedto effect the compression stroke of the piston assembly.

The invention will be described with reference to the accompanyingdrawing, in which- Figure l is a longitudinal sectional elevation of afree piston structure incorporating the spring arrangement of thepresent invention,

Figures 2, 3, 4, and 6 are partial longitudinal elevations of modifiedforms of the arrangement,

Figure 7 is a partial sectional elevation of the arrangement of Figure 5in another position, and

Figure 8 is a partial sectional elevation of an associated startingdevice.

Referring to Figure 1, 1 is a power cylinder and 2 and 3 compressorcylinders axially arranged with respect to the power cylinder one ateach end thereof, the compressor cylinders being of larger diameter thanthat of the power cylinder. A pair of piston assemblies each comprisinga power piston 4 and a larger diameter compressor piston 5 arereciprocatingly mounted in the cylinders, all in accordance withconventional practice. In the structure shown, the general frame of themachine includes an inner aligning disc 6 for each compressor cylinderwith air inlet openings 7 therein, an outer closure plate 8 with valvecontrolled compressed air outlets 9, a cover 10 forming a compressed airpassage 11, and a duct 12 leading from passage 11 to an air intake 13 inthe power cylinder. Also, as shown, each compressor piston has valvedopenings 14 therein and the power cylinder has a fuel injection nozzle15 and a scavenging air outlet 16.

In accordance with the invention, a hollow cylindrical member or sleeve17 is mounted in each cover member 10, such sleeve having a portionextending partially into a cylindrical recess 18 in the adjacentcompressor cylinder and in which it has a sliding t. A compressionspring 19 is positioned within the sleeve 17 and recess 18 and has I oneendseated on an annular flange 20 carried 'by the outer end of sleeve 17and its other end engaging a seat 21 fixed in piston .5 at the base ofrecess 18. As shown, v

the recess 18 is open to atmosphere through the open end of the sleeve.It will be apparent that, on the firing stroke of the piston assemblies,the springs 19 will be compressed" and, on completion of the firingstroke, will function to move the piston assembliesv inwardly to performthe com#v pression stroke thereof. It will be understood that springs ofsuitable strength to carry out this step will Abe lemployed. l l

An advantage of the structure described resides in the fact that asubstantial interior area vof the piston assembly? is exposed toatmosphere and facilitates a cooling of the y pistons. This exposed areaalso makes possible the proi 22 is located betweenthecoinpressor pistons5 and has" its ends connected to the confronting faces'of such pistonsas by rods 23. v l

In the modificatonof Figure 4, a4 separate tension spring 24 isconnected to the inner faceof each compressor piston 5, the inner endsof both springs being attached to a frame member 25.

It will be understood that a plurality of springs 22 or pairs of springs24 may be symmetrically arranged about the axis of the pistons.

Figure 5 shows an arrangement wherein, instead of the tension spring 22,a compression spring 26 is arranged to act as a tension spring. Asshown, the spring is received within a tubular member 27 with one endthereof seated on an annular flange 28 at one of the members, the otherend of which is connected to one piston 5 as by a rod 29. A rod 30connected to the other piston 5 extends through the member 27 and spring26 and has a cross bar 31 on which the other end of the spring isseated. This arrangement may be desirable under certain circumstancessince compression springs have greater fatigue characteristics thantension springs, particularly at high speeds.

Figures 6 and 7 show a modification wherein a conical coil compressionspring 32 is interposed between the outer face of each piston 5 and theclosure plate 8. This arrangement is possible because of the relativelysmall space required by use of such a spring.

Figure 8 illustrates a manner of associating starting device with astructure such as shown in Figure l. A rod 33 is mounted axially withinthe spring 19, sleeve 17, and recess 18 by screwing its end portion intothe piston wall at the base of the recess as indicated at 34. The rod 33has a screw-threaded portion 35 projecting outwardly from the recess andmounted thereon is a hand wheel 36 the hub portion of which engages thespring retaining ange 20. To start the engine, the hand wheel 36 isturned to reciprocate the rod 33 outwardly bringing with it the piston 5while compressing spring 19. When the pistons are in outermost position,they may be locked therein by means of a detent which engages the teethof a pinion 38 forming part of a piston synchronizing means which alsoincludes a rack 39. The rod and handwheel may now be removed from eachpiston assembly and, on tripping the detents, the springs 19 force thepiston assemblies together rapidly to sta-rt the engine. It will beapparent that the use of piston return springs, as described, makesreadily possible such an engine starting procedure as well as othersimilar engine starting prov cedures,

Patented Nov. 17, 1959 Y YWhile a single helical compression spring 19is shown for use in an embodiment such as illustrated in Figure l, itwill be understood that such spring may be of either unitary orcomposite form. '-fMoreover, in order to provide adequate energy'and/orto avoid surgi-ng under high speed, a plurality of springs'niay beassociated together in various arrangements, three of which areillustrated in Figures 9, 10 and 1l by way of example.

Figure 9 shows a pairY of concentric'ally arranged springs 40 andv 41with opposed helix angles.

Figure l() shows a pair vof concentrically arranged springs 42 and 43with their helices wound in the same direction. I

Figure ll shows a pair of springs 44 and 4S of the same pitch and meandiameter threaded together.

A It will be understood that any suitable spring stock cross section maybe employed for the springs.-

Moreoven the coil pitch and/or mean diameter of the springs may bevaried as desired to reduce spring surge where the engine speed is suchas to induce springA surge.

Dampening of spring surge may also be accomplished by allowing thesprings to rub against their guides or in multiple spring installationsagainst each other. Furthermore,- combinations of pitchvariation, meandiameter variation, and frictional contact may be employed to avoidspring surge.

I claim:

1. In a free piston machine having a power cylinder, compressorcylinders; a pair of piston assemblies mounted in said cylinders, and acover enclosing the end of each of said compressor cylinders, saidpiston assemblies being movable towards each othersto perform acompression stroke and away from each other to perform a tiring stroke,each said piston assembly having an axial recess in the outer facethereof, a sleeve ixed to each said cover and projecting into saidrecess for sliding engagement with the wall thereof, and at least onespring in said sleeve and recess and bearing upon an inner face of oneof said piston assemblies to urge said piston assemblies towards eachother to perform said compression stroke, said springs being loaded inresponse Ito said firing stroke to constitute a source of energy forperformance of said compression stroke.

2. A free piston machine as dened in claim l, including means for movingeach said piston assembly against the action of said spring comprising arod extending axially through said cover and spring and having one endbearing on said piston assembly, and a'member threadedly mounted on saidrod exteriorlyA of said cover.

References cited in the fue of this patent UNITED STATES PATENTS 790,325Steele as May 23, 1905 FOREIGN PATENTS 353,587 Germany May 22, 19221,119,336 France Y. Apr. 3, 1956

